Republican presidential hopeful businessman Donald Trump fields questions at The Family Leadership Summit at Stephens Auditorium on July 18, 2015 in Ames, Iowa. According to the organizers the purpose of The Family Leadership Summit is to inspire, motivate, and educate conservatives. (Credit: Getty Images / Scott Olson )

Some Republicans gleefully scripted Donald Trump's political obituary in the wake of his scathing comments about Sen. John McCain's military service earlier this month, hoping that his freewheeling presidential campaign had finally imploded.

Predictions of his demise were apparently premature. Instead, Trump is gaining momentum ahead of next week's first Republican debate, a new Reuters/Ipsos opinion poll shows.

The poll shows Trump with his greatest support yet nationally, as nearly a quarter of Republicans surveyed said he would be their choice as the party's presidential nominee in 2016. He has opened up a double-digit lead over his closest rival, former Florida governor Jeb Bush, who trails at 12 percent.

"I'm proud to be in first place by such a wide margin in another national poll," Trump said in a statement to Reuters.

Trump has surged since suffering a slight downtick in the wake of the McCain furor. The five-day rolling online poll had the real-estate mogul and reality TV star at 15 percent among Republicans on Friday before rocketing to 24.9 percent on Tuesday.

"He's not going away," said Steve Duprey, a Republican National Committee member from New Hampshire and a former McCain adviser. "There are people who think his candidacy is a flash in the pan or a flash in the moment, but I think that underestimates his appeal."

Trump would seem to be a lock to be on the stage next week in Cleveland for a debate sponsored by Fox News, which will use national polls to determine which 10 of the 17 Republican candidates in the field can participate.

But perhaps of greater concern to establishment Republicans, Reuters/Ipsos polling also shows that in a three-way race with Trump running as an independent in the general election, Trump would drain support from the Republican nominee and allow the Democrat, likely Hillary Clinton, to skate to victory.

Trump has refused to rule out a possible independent run. In a matchup with Clinton and Bush, he would essentially tie Bush at about 23 percent among likely voters, with Clinton winning the White House with 37 percent of the vote. (About 15 percent of those polled said they were undecided or would not vote.)

It is that scenario that should keep party strategists up at night. Something similar occurred in 1992, when businessman Ross Perot's independent candidacy helped thwart President George H.W. Bush's reelection bid and allowed Bill Clinton to capture the presidency with just a 43 percent plurality. Bush received the lowest percentage of the popular vote of any sitting president in 80 years.

CORNERING THE MARKET

In Trump's case, he appears to be cornering the market on white voters, the backbone of the current Republican Party, the poll shows. Republicans need as many white votes as possible to offset demographic shifts in the United States that have handed Democrats an electoral advantage in the last two presidential elections.

In 2012, Republican Mitt Romney won almost 60 percent of the white vote, yet still lost to President Barack Obama by five million votes.

A third-party bid by Trump would effectively doom any Republican's chances at the presidency, the poll shows, be it Bush, Wisconsin Gov. Scott Walker, Florida Senator Marco Rubio or someone else.

John Geer, a political scientist and an expert on public opinion at Vanderbilt University, said the poll results make sense in light of Trump's appeal to conservatives who believe the party nominated two moderate establishment candidates in McCain and Romney.

"The activists are doubly angry," Geer said. "He's capturing that anger. They're looking for a voice, and he happens to be here at the right time."

But John Feehery, a Republican strategist in Washington, cautioned not to place too much stock in Trump's surge, arguing it is largely a function of the name recognition he enjoys in light of his celebrity.

"This is just 24 percent of a Republican electorate, probably most of whom probably haven't thought much about the presidential race, have a visceral reaction to Bush, and haven't really heard about the other candidates," he said.

He expects Trump's numbers to fall as the race intensifies and scrutiny of his candidacy increases.

"The curtain has not been pulled back yet," Feehery said. "In time, people will see Trump is not who they want to have as a nominee. But that's going to take awhile."

The five-day rolling poll was based on a survey of a 425 Republicans and has a credibility interval of plus or minus 5.5 percentage points. The three-way race poll, taken at the same time, used a sample of 1,280 Americans and has a credibility interval of plus or minus 3.1 percentage points.